Idiopathic Respiratory Distress Syndrome (IRDS) remains a major cause of neonatal death in the United States. Several biochemical assay techniques are excellent for determining that the lungs are mature after the fact, but the value of the assays for prediction of future dates of maturation or potential to respond to glucocorticoid treatment is quite limited and the necessary amniocentesis is an invasive procedure. We are examining the use of noninvasive diagnostic ultrasound as an in utero, predictive test of the occurrence of IRDS following delivery. Preliminary work on fetal sheep under ideal experimental conditions indicated a strong correlation between our quantitative and visual analysis of backscattered ultrasound and the fetal lung's morphological and functional maturity. We have undertaken clinical studies with visual interpretation of fetal lung and liver images. Convenient RF data acquisition and analysis systems and software have been developed for evaluation of the predictive power of quantitative measures of ultrasound interactions in fetal lung. There is considerable spread in both the visual and initial quantitative ultrasound measures vs L/S ratio or estimated gestational age. However, in the visual data where 18 patients have been examined reliably more than once, there is a consistent reduction in lung to liver echogenicity over examination time intervals exceeding 21 days. In the proposed continuation project, over 500 patients with expected normal fetal lungs and 80 insulin-dependent diabetics will be studied. In addition to existing measures, we will test the predictive value of quantitative relative lung to liver backscatter, scatterer spacing, and two-parameter attenuation. Lung deformability in the presence of heart motion will be assessed visually and by cross-correlation and tissue motion detectors. These measurements plus extensive correlative data will be stored in the existing database management system for correlation of the ultrasonic estimates of tissue properties with other morphological, biochemical and functional measures of lung maturity. The potential for greatly improved quantitative ultrasound measures of fetal lung structure will be assessed by phantom and tissue sample tests of a phase-insensitive receiver system.